Galaxy clustering and dynamics from redshift surveys

Abstract

The clustering and dynamical properties of the 368 galaxies in the redshift surveys of Metcalfe et al. (1989) and Parker et al. (1986) are investigated. These galaxies were selected from ten high galactic latitude fields complete to a magnitude limit of m(b(_J))<17(^m). These complement the five similarly selected fields in the survey of Peterson et al. (1986) and so the overall clustering and dynamical properties of all three samples are discussed. Initial studies of the distribution of galaxies in the survey of Peterson et al. were carried out by Bean (1983). This thesis extends that earlier work by examining the conclusions of Bean in the larger volume of the new surveys considered here. It is found that, whilst the combined estimate of the line-of-sight peculiar motions in the three samples together is in reasonable accord with that found previously, the range of peculiar motions in the individual samples is larger than previously anticipated. The rms pair-wise velocity (w(^2))(^1/2) is found to be (w(^2)(^1/2)=(600±140)kms(^-1) in the Metcalfe et al. survey as compared to (w(^2))(^1/2)=(0±240)kms(^-1) and w(w(^2))(^1/2)=(190± 90)(^-1) in the Parker et al. and Peterson et al. samples, respectively. These estimates of the motions of galaxies at spatial scales of ~1h(^-1) Mpc (H(_o)=100kms(^-1) Mpc(^-1)) together with measures of the clustering provide constraints on the mean mass density of the Universe through the Cosmic Virial Theorem. It is found that the mean mass density parameter for the three samples considered as a whole is Ω(_o)=0.18±0.09, on the assumption that galaxies trace the mass distribution, and this constraint is similar to that obtained previously mainly because of the larger range of peculiar motions found. The clustering distribution of the galaxies in the new samples was investigated on spatial scales ranging from a few up to -l00h(^-1) Mpc. It was found from the number-redshift and number-magnitude counts that these samples were fairly homogeneous at the largest scales and in good agreement with previous results from the Peterson et al. catalogue. Thus using these samples to estimate the mean clustering properties of galaxies, it was found, from the two-point correlation function ~5(s), that the galaxies in the new samples appear to exhibit a preferred clustering length at -2h(^-1) Mpc and this confirms the 'shoulder ' detected in the correlation function of the Peterson et al. data by Bean (1983). On the basis that this shoulder is a real spatial feature (and not caused by peculiar motions) the mean clustering length of galaxies in the three samples is r(_o) =(6.6±0.5)h(^-1) Mpc in the range 2<s<7h(^-1) Mpc and this is significantly larger than the r(_o) =5h(^-1) Mpc that was previously thought to apply to galaxies in this region of separation. At scales larger than -7h(^-1) Mpc the correlation function in the combined sample of the three surveys indicates that the galaxy distribution rapidly approaches homogeneity. Although there are some tentatively detected spatial scale lengths in the galaxy distribution at these larger scales, the main conclusion from the correlation function for these galaxies is that there is no evidence of large-scale clustering at the 2 sigma statistical significance level from separations of -10 to 100h(^-1) Mpc. Thus on the assumption that these galaxies trace the mass distribution this implies that the Universe is homogeneous to -15% at these scales. Finally, some new redshifts of galaxies were presented that were observed with the FLAIR spectrograph on the UK Schmidt telescope. These observations indicate that this instrument is capable of performing systematic redshift surveys of m(b(_J))<17(^m) galaxies with a completeness of -80% and with an accuracy in redshift velocity of ±150kms(^-1) rms. This will then pave the way for future large area redshift surveys in the southern hemisphere.